The overall goal of this investigation is to study the binding of specific drug ligands to the serum of the fetus and neonate. C14- Pentobarbital and C14-salicylic acid binding will be studied in vitro by equilibrium dialysis in the sera of fetal, newborn and adult goats, dogs, guinea pigs and rabbits. Serum proteins will be quantitated by microzone and polyacrilamide disc gel electrophoresis in these species as well as in porcine and human sera. Porcine, human, and caprine sera will be analyzed by immunoelectrophoresis. The possibility of binding of these ligands to serum fractions other than albumin will be investigated. Emphasis will be placed on proteins specific to the fetus (alpha2-fetoprotein and fetuin) and on proteins known to sequester drug ligands (alpha2-macroglobulin). Binding will be studied in serum depleted of specific fractions by polyethylene glycol precipitation or by immunochemical methods. Binding fractions will be isolated, purified, and subjected to equilibrium dialysis binding assay. Immunoelectrophoresis and autoradiography using H3- labelled ligands will also be employed to identify binding fractions. An additional study is designed to determine whether or not the capacity of porcine albumin for binding C14-pentobarbital changes with age.